Balsa Fuel Tank?

There are high penetrating epoxy resins available, but I've not seen them sold in reasonably small quantities (most usually available from marine related manufacturers) and they are expensive. Secondly, I would not be inclined to add a solvent since a solvent may render the epoxy brittle.

My inclination would be to mix a batch of 30 minute epoxy, apply a coat to all interior surfaces of the tank, then use a heat gun to warm and thin the epoxy to allow it to soak into the wood. I've done this routinely over the years to fuel proof firewalls and tank compartments. When warmed, you can see the epoxy being drawn into the underlying wood or plywood. The 30 minute resin will remain workable for a longer time even when heated. When cured, you will have to clean the surface to remove any amine blush that may have built up before applying a second application, if needed. Sometimes, the first application will soak in so well that it will leave pinholes and will need another coat.

Once you're satisfied that the interior walls are well fuel proofed, then clean the surfaces well and epoxy the tank together, making sure that each joint has a small fillet of resin.

I applied thinned 24 hr epoxy on parts and vacuumed.

Assembled box, opened fuel tubing holes and sanded the out of box. Then applied second thinned epoxy coat to inside of box and cover.

After drying I'll epoxy tubings and glue cover on box. Then will apply two coats epoxy on out of box.

It is very simple

Hi Levent! Lots of interesting ideas! I liked what Andrew had to add.. about the balsa absorbing the epoxy through heat.. and possibly needing a 2nd coat. That would make for strong panels that are impervious to glow-fuel (up-to a certain percentage of Nitro).

Will you be testing/fueling your tank Levent? Maybe bench-run an engine?

Hi Rod, yes I appreciate Andrew's comment. I am going to apply third coat of thinned epoxy on inside. I'll also brush epoxy on outer surfaces three times, last coat will be metal epoxy. I'll smear metal epoxy coat like as a putty.

Yes, I am going to fill it with raw fuel and test it for a month. I also want to try it with a running engine to test against exhaust gases, but how many times I need to test it I don't know. One or two runs is enough to test the tank?

I forgot to ask: Does epoxy affect by nitromethane or methanol? Or both?

Levent Suberk wrote:Hi Rod, yes I appreciate Andrew's comment. I am going to apply third coat of thinned epoxy on inside. I'll also brush epoxy on outer surfaces three times, last coat will be metal epoxy. I'll smear metal epoxy coat like as a putty.

Yes, I am going to fill it with raw fuel and test it for a month. I also want to try it with a running engine to test against exhaust gases, but how many times I need to test it I don't know. One or two runs is enough to test the tank?

EDIT: not sure.. but I would say that higher-nitro would be the cause of any eroding tank-innards.. rather than the Methanol.

I don't know a method for testing your tank's construction against breakdown from glow-fuel. You mentioned using AL tubes to plumb the tank. I don't know how they'd react to your glow-fuel mix. I prefer Copper tubing. The automotive parts-stores sell coils of 1/8"-3mm Copper tubing for connection to oil-pres. gauges.. etc. Expensive.. but worth the $$ if you get into building tin-plate hard-tanks!!!

I wish I could offer comments about fuel resistance in tanks, but my experience has been limited to firewalls and tank compartments. These are areas that I usually would wipe down at the end of a flying session, consequently, they were not subject to long term immersion. I would think that evacuating the tank with a syringe as much as possible, then using a high volume syringe to blow air into the tank to help evaporate the methanol and nitro before putting the plane away might extend the tank life. I do this even with plastic tanks.

Vinyl ester resins are touted to be gasoline/ethanol proof, but are pricey, smelly and usually fairly thick. These resins are catalyzed with MEKP (nasty) at very small percentages which would make mixing a small batch difficult. Polyester resins (we sometimes call them laminating resin) would be totally unsuitable.

I believe Levent's approach of saturating the wood and finishing with a surface coat is about the best any of us could do. The only other method would be to construct a tank from .5 oz fiberglass cloth, but this would likely be much more difficult than building one from brass or tin sheet.

Thanks Andrew for fuel tank tips.

Thinned 24 hr epoxy need time to cure. Waiting coats to dry. I am going to apply third thinned coat to inside of fuel tank and install fuel tubings at tomorrow.

My planned progress is:

1- All parts covered and vacuumed with 24 hr thinned epoxy
2- Parts assembled to form a box
3- Inside of fuel tank box brushed with 24 hr thinned epoxy
4- 3 repeated
5- Metal tubings installed with 5 min metal epoxy and cover glued on box with 5 min metal epoxy
6- 24 hr thinned epoxy applied on outside of completed box
7- 6 repeated
8- Thinned metal epoxy brushed on outside of box

Steps 4 & 5: Applied third coat of alcohol thinned 24 hr epoxy and installed fuel tubings with 5 min epoxy. Cover will be glued.

Note: Upper tubing is fill line.

Looks good Levent ,, i think if there is a weak spot it will bee the epoxy joint .

Last epoxy coat drying. Tubings closed with tape.

Looking good. A very interesting subject, and well executed!

Fuel tank finished. I think that last coat metal epoxy is a little heavy. 24 hr or 30 min thinned epoxy must be used instead of metal epoxy. Total weight is .547 oz.

Nice Levent.  "Proof of concept" or it will be as soon as you fuel it up and see how it stands up.  

Think of the possibilities. wedge tanks, rectangular, square......sizes and shapes adapted to fit a particular model.  Balsa easier to work with than tin and solder.  But I was thinking, couldn't you achieve the same results by simply air brushing on several coats of two part epoxy paint before, during, and after assembly eliminating a whole lot of work and time?  I used that approach on one of my scratch built models and fuel hot or cold never bothered it.

Ah, found the picture I was looking for. Recent picture, plane at least 30 years old multiple flights, Epoxy paint.

Thanks.  You are right about using epoxy paint, however I can't find epoxy paint in small quantities.

I am going to try it with Morgan Fuel Sidewinder Race %15 nitro raw fuel.

Nice !! Hope it holds up ,, yes the concept of building a tank to fit or of certain size is really cool !!